Dielectric study in nanocrystalline Bi4Ti3012 prepared by chemical coprecipitation

Bi4Ti3O12 nanoparticles were synthesized by chemical coprecipitation and crystallized in the perovskite structure after calcining at 520 degrees C. The dielectric properties were measured in bulk nanocrystalline compacts with different grain sizes. It was found that there were three peaks in the curves of the dielectric response as a function of temperature. The first peak shifts to higher temperature with decreasing grain size, which is considered to originate from the polarization of the ions in the conductive (Bi2O2)(2+) layers across the potential barrier of the weak conductive perovskitelike layers. The second peak, contributed by the polarization of the defect dipoles on the grain surfaces, especially Bi-i-V "(0) dipoles, decreases gradually in intensity and finally disappears with increasing grain size. The last one, corresponding to a ferroelectric phase transition temperature, increases at first with decreasing grain size from 56 to 25 nm, then decreases with further decreasing grain size, and the mechanism is correlated with a competing effect of the released internal stresses and the clamped domain walls due to the diffusion of oxygen vacancies. (C) 1998 American Institute of Physics.